The present invention relates generally to filter media and particularly to a disposable type particulate filter media for use in kitchen range hood applications wherein the media is exposed to oil and fat aerosols. Typically, range hoods include a motor driven fan to draw cooking aerosols and associated particulates in the air stream through a filter pad supported in the range hood to entrap the oil and fat type aerosols created during the cooking process. Such aerosols are often referred to as grease and include those oils and fats which are liquid and solid at room temperature.
Prior disposable filter media for range hood cooking applications have consisted of synthetic fiber type filter pads or a combination of materials predominantly employing non-woven synthetic fibers formed into a relatively dense mat or pad having relatively small interstices between the fibers for the passage of air. These types of filters do satisfactorily entrap the oil and fat aerosols. However, in this type of filter there is a tendency for the aerosols to be deposited on the fibers where they tend to locally agglomerate and are not spread evenly throughout the filter pad.
A relatively dense non-woven synthetic fiber pad is particularly necessary when the pad is provided with printed indicia to provide a relatively visual distinct pattern to indicate in some manner that the filter has become loaded to the point requiring replacement.
U.S. Pat. No. 4,336,038 illustrates such a prior art nonwoven synthetic fiber filter mat provided with means to visually signal a given loading of the filter with oil and fat aerosols. This patent discloses a system wherein a mixture of two dye components, one oil soluble and the other oil insoluble, are used to print a selected pattern of the mixture on the face of the filter. The purpose of this system is to provide a visual color change from the initial predominant oil insoluble component to the less dominant oil soluble dye component upon loading of the filter with oil and fat aerosols.
However the oil insoluble dye component may prematurely bleed when introduced to water vapor in the form of steam or high humidity formed in ordinary cooking processes and distort the original pattern. This could lead to a confusing visual signal to the untrained user. Additionally, the desired visual signal consists of the bleeding of the oil soluble component into relatively small uncolored spaces between the printed pattern and requires a visual judgment which may be difficult for the uninitiated user as to just when the desired limit of oil and fat loading of the filter has been reached.
Further, the relatively dense nature of such a predominantly non-woven synthetic fiber pad raises the pressure drop across the pad and therefore draws less air flow through the pad for a given size range hood fan. The relatively dense nature of the pad required to permit printing of easily recognized indicating indicia on its face is disadvantageous to the efficiency of drawing the particulate laden air produced during the cooking process through the filter.
A range hood filter pad which incorporates a reliable visual signal to the user indicating replacement is due and which possesses a relatively low resistance to air flow, yet efficiently filters particulates has not been developed by those skilled in the art.